Developments in using off-line radio frequency impedance methods for measuring the viable cell concentration in the brewery

The radio frequency (RF) impedance method of measuring yeast concentration is accepted in many breweries around the world. The method relies on detect ing the capacitance of the yeast cell membranes and gives a rapid linear re sponse over a wide concentration range. The main application for the RF imp edance method is for measuring the concentration of viable yeast in slurrie s; however the data presented also illustrate the use of the method for mon itoring the yeast concentration during production fermentations. The variab ility of yeast growth during small-scale fermentations was also investigate d for two lager strains. Batches pitched on the basis of capacitance were c ompared with those pitched using the traditional basis of wet weight. The s mall-scale fermentations pitched on the basis of capacitance were more repr oducible than the fermentations pitched on the basis of wet-weight yeast. G ood correlation was found between the capacitance and hemocytometer techniq ues in most small-scale and production vessels when the cell diameter was a bove 6 mu m.